1. Field of the Invention
The present invention relates generally to a method for creating an oxygen barrier film, typically a polymer film, by means of coating the film with a barrier coating containing a copolymer of maleic acid and acrylic acid in combination with a film former, such as polyvinyl alcohol. The barrier coating, which is preferably transparent, is also disclosed.
2. Description of Related Art
Barrier coatings are desirable for many applications, such as food packaging and other product packaging. These barrier coatings minimize transmission of oxygen, and water vapor to varying degrees, through the coated substrate. For many end uses, it is desirable for the coating to be clear. When the substrate is also clear, as in a transparent polymer film, view through the substrate is not obstructed. However, known barrier coatings have suffered from numerous limitations, including high cost, inadequate transparency and limited barrier properties. There is a need for barrier coatings that address one or more of these problems. A need also exists for barrier coatings that are adapted for application to polymer film substrates. Coatings adapted for in-line application during film manufacture are also desirable.
A standard barrier coating includes polyvinylidene chloride. Such a coating is typically solvent based, which may render the associated coating processes environmentally hazardous. In addition, because of possible solvent residue in the coating, these polyvinylidene chloride coatings may pose some risk when used to package food items. These coatings also are not reclaimable, and decompose to give off HCl vapors if recycled. Furthermore, such coatings are coated off-line after film orientation is complete. This usually requires thick coatings that are not economically optimal, and additional processing steps that render the coated film more expensive.
Known barrier coatings also include certain polyvinyl alcohol poly(meth)acrylic acid-based coatings. These coatings apparently require very substantial heat treatment and substantial coating thicknesses to achieve good oxygen barrier properties. Furthermore, such coatings are coated off-line after film orientation is complete. This requires additional processing steps that render the coated film more expensive.
Accordingly, it is an object of the present invention to provide a barrier coating suitable for application to a base polymer film.
It is a further object of the present invention to provide a base polymer film with a barrier coating on one or both sides.
It is another object of the present invention to provide a barrier coating that is substantially free of streaks and smears, particularly when applied to a base polymer film.
It is yet another object of the present invention to provide a barrier coating that is substantially transparent.
It is a further object of the present invention to provide a barrier coating having good oxygen barrier properties.
It is another object of the present invention to provide a barrier coating that is cost efficient to make and apply.
It is a further object of the present invention to provide a barrier coating that is suitable for food packaging.
It is another object of the present invention to provide a barrier coating that performs well at high humidity.
It is a further object of the present invention to provide a film that when metallized provides improved barrier properties.
The present invention has accomplished these objectives by providing in a preferred embodiment a coated polymer film having a coating that includes a copolymer of maleic acid and acrylic acid in combination with a film-former, preferably polyvinyl alcohol. This coating is applied thinly, preferably via in-line coating methods, to achieve a thin coating that provides good oxygen barrier properties.